The present invention relates to a device and a method for localizing terminal devices and in particular to how wirelessly communicating terminal devices may be localized and reliably with a high precision, wherein a continuous updating of models of changing ambient conditions is guaranteed.
In a few years the (self) localization of mobile devices or terminal devices, respectively, will be one of the most important fundamentals for modern, user friendly applications. Due to the continuously increasing distribution of handy mobile devices (e.g. PDAs, smart phones) in connection with the exhaustive availability of digital or analog transmission technologies (e.g. WLAN, UMTS, GSM), the market for applications grows supplying location relevant information to the user in every situation. Applications nowadays are mainly based on the satellite navigation systems NAVSTAR-GPS. The same may, however, in the inner city area with high buildings, tunnels and bridges, and in buildings (e.g. airports, railway stations, exhibition centers) often not provide a position, or only a very inaccurate one, as the satellite signals are attenuated or influenced too strongly. In particular these locations, however, distinguish themselves by a high number of visitors. An alternative, low cost and reliable location technology is, thus, essential which takes this scenario into account.
For the wireless network connection of portable devices, the WLAN standard, according to IEEE 802.11 (a, b, g) established itself. The same is continuously further developed, both with regard to data rate and also range. The established standards, as well as the standard 802.11n which is still in its design phase, enable a wideband data transmission with high data rates and distinguish themselves by a high integration degree, which enables a low cost hardware. In today's PDAs and smart phones wireless interfaces such as the above mentioned WLAN are usually integrated. In addition to this, often Bluetooth, and in future, possibly also WIMAX will be used.
In the case of WLAN, in the meantime, commercial, public WLAN hotspots are available in many locations with a high number of visitors. In addition to this, the strongly increasing distribution of wideband Internet connections (for example via DSL) also in the private area supported the distribution of WLAN as an advantageous home networking technology. Several studies indicated that the inner city area is, in many places today, already virtually exhaustively supplied with WLAN or even excessively covered. In particular places of daily life and of interest to tourists are well equipped in this respect.
It is currently of an advantage to use WLAN as a base technology for location. In future, of course also other technologies will be used to which the inventive concept discussed in the following may also be applied. The location in WLAN networks may, in principle, be executed by assessing the received base stations (hotspots or access points, respectively), wherein for example, the signal strength of the same received on the respective terminal device is assessed. WLAN signals are, however, strongly shielded by buildings and other obstacles, wherein in particular in areas with a broad WLAN supply usually no ideal free field conditions exist, as they are located in the city area. Thus, the distance to a base station or another communication partner may not be directly concluded from the measured signal strength or field strength, respectively. A public environment and/or surrounding or a dynamically changeable surrounding (for example a storage building) is basically subject to non-influenceable changes (setup/dismounting/exchange of access points, only temporarily limited activity of the access points, etc).
One possibility to control the complex ambient conditions which result in the non-free field applications is to determine the actual signal propagation by test measurements at geographically known reference points or reference positions, respectively. A location on the terminal device may take place by matching currently recorded measurement values to stored measurement values of the reference point data sets. From the best match or the reference points which are most suitable, respectively, a position is then estimated without any knowledge about the actual location of the base stations or the access points, respectively, being needed.
In an urban environment shaped by continuous changes of the environment, from the use of such a learnt method (also referred to as the reference point or fingerprinting method) the following problem results. The data base with reference values or the reference data, respectively, are initially detected and later have to be continuously or repeatedly updated. In other cases, the expressiveness of the reference data decreases—they “age”—and the location quality will suffer as the receive conditions or the ambient conditions, respectively (recordable ambient information), change over time.
While the fingerprinting method per se functions, the central problem is updating the reference data. To keep the effort for setup and maintenance of the database or the reference data, respectively, limited, partially methods were proposed in which all users may remove gaps and errors in the database by “catching up”. A problem with this approach is the exchange and the trustworthiness of data arising in this manner. To keep the system functioning, it has to be prevented in any case that accidental erroneous measurements (e.g. when a user indicates a wrong current position when catching up) and also conscious acts of sabotage make the common database unusable. Existing approaches for WLAN location designed for the use in open surrounding (such as e.g. Place Lab or Skyhook Wireless) use triangulation instead of fingerprinting as a basic method, with the above-described disadvantages. Thus, these methods need a database in which an assignment of location information of the base station to its base station identification is executed (e.g. using the MAC address of the base station or the access point, respectively). From current measurement values, distances to several base stations are estimated and a position is calculated therefrom. In these systems, thus also the setup of a secured, reliable database is needed.
The problem of trustworthiness of learned information and a modeling of the dynamic changes of the surroundings have thus far only been insufficiently solved. Place Lab converts and imports existing databases with base station locations, e.g. of hotspot operators or from War-Driving-Community. War-Driving is the targeted driving of streets of houses with the object to find WLAN stations and supply them with a location reference. War-Drivers for this purpose use a WLAN capable laptop which is additionally equipped with a GPS receiver. The problem here is that an up-to-datedness of these data, in particular with regard to private stations, is not guaranteed. Simultaneously, precision and trustworthiness of this method are doubted.
Skyhook wireless attempts to solve the problem by the cooperation of so-called “scanners”. The same are especially selected, trustworthy users which service the database by a target War-Driving. By this, keeping the database up to date is connected with a high effort and a fast adaptation with changes of access points is not possible. Skyhook Wireless currently offers its customers an annual update of the database. Nevertheless, so that the database does not age too fast, Access Point which do not belong to public hotspots of large providers (which are thus potentially continuously in operation and firmly installed in one location) are excluded from the system. Thus, however, the coverage clearly decreases as currently already a great number of the installed WLAN base stations are of private non-public nature (SOHO, Industry, etc) and as far as possible defy control and information supply.
Further location or positioning solutions, respectively, which allow all users to maintain the database rely on a sense of community of the users and thus do not consider a possible conscious tampering with the database.
The above-described, already partially used methods may only update the database in large temporal distances. Thus, this offers no reasonable way of handling or, respectively, no worthwhile concept for dealing just with temporally active stations.
This problem is especially relevant for private stations which represent a strongly growing part of the stations, as such private stations are frequently only operated on demand due to concerns with regard to the danger of a break in into the WLAN network, or due to the exposure to radiation. The solutions implemented thus far do not permit, in particular in the interesting urban area in which on the one hand the conditions for receiving for a triangulation are too difficult and on the other hand the available base stations or communication partners, respectively, frequently change, to perform a localization of terminal devices without executing the use of external positioning systems reliably.